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Acer AL1916W - Two seconds to black - Voltage regulator problem?

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    Acer AL1916W - Two seconds to black - Voltage regulator problem?

    Hello all. Excellent forum you have here - it has already been a great help to me. I am posting the details of my situation before I go and start buying parts to see what suggestions the great minds here may have on diagnostics or otherwise.

    I have an Acer AL1916W monitor which has recently failed in the following way: the screen comes on at power on, but after a couple seconds the screen goes black. Using a flashlight, I can easily verify the LCD is fine but there is simply no backlight.

    The power supply board is of the type ILPI-025 Rev C (Date of manufacture was 2006.07.28)

    I've attached the following 4 pictures for reference:
    Figure 1: Component-side view of power supply board
    Figure 2: Solder-side view of power supply board
    Figure 3: Annotated solder-side view of power supply board
    Figure 4: Close-up view of problematic voltage regulator. The one on the top left is bad; the two that share the heat sink closer to the foreground are fine.

    I have heard there is a common issue where capacitors could malfunction and cause this issue. I see no signs of damage to any capacitors on the power supply board. (No bulging, no leaked electrolyte. Maybe some have pushed away from the board, esp. the 25V 47uF ones: C807, C820, C827)

    With no power, the resistance was measured across the transformers SPW-068. The voltages measured between S1-S1 and S2-S2 were 628 and 618 Ohms. They are not shorted and they are pretty close to each other, so it seems okay.

    With no power, I measured no resistance across the two fuses I was able to see on the board (F801) so these have not blown

    I did some more tests with the power connected. Note, the ribbon from the decoder board to the LCD was disconnected, and so were the CCFL lights. I confirmed there is AC power at 120.3 V across the rectifier supply (S3-S3). I confirmed that I have 160.5 VDC at the output of the rectifier (S4-S4).

    I checked the standby voltage and the power on feedback voltage from S5-SG and S6-SG respectively (note: the pinout is mislabeled on the solder side of the board – pin 1 and pin 2 are both 5V-standby. I measured with reference to a chassis screw mount for convenience). Here I confirmed a stable 5.15V standby voltage and the power on feedback voltage at pin 4 was briefly 3.2V when powering on, before it recognizes there is no input and goes back to the low 0.04V condition. Okay nothing out of the ordinary here.

    I checked the output of the three voltage regulators on the board. The regulators labeled S7 and S8 were both very stable at 5.15 and 14.27 V respectively. These were the same when measured with reference to the pin just above or just below the labelled middle pins. However, the other regulator at S9 was decidedly unstable. I am not sure what voltage it is supposed to output, but I had my meter in 200V mode and I was seeing numbers all over the place between 0 and ~60.

    The bad regulator also behaves differently from the two good ones when I probe the resistance across the pins. I will number the pins from 1 to 3 starting from the top in my picture of the solder-side of the board. All of them have the regulated volts on pin 2. If I probe resistance for pins 1-2 and 2-3 on any of the three regulators there is a high but measurable resistance (i.e. 1.5k – 150k) which steadily increases while probing it. The resistance for pins 1-3, however, was only 0.4 Ohm on the two good regulators, but it was 9.1 kOhm on the bad regulator.

    I am not sure where I should go from here? Is this a sign that the regulator itself should be replaced? Could it just be a problem of the nearby 25V 47uF capacitors (C807, C820, C827)? Are there any more diagnostics anyone could suggest?

    Thanks for reading
    Attached Files
    Last edited by Long AMD; 09-13-2020, 06:02 PM.

    #2
    Re: Acer AL1916W - Two seconds to black - Voltage regulator problem?

    Your so called S9 is not a regulator, it is the drain of the primary mosfet and will have around 160vDC plus the switching pulse. This is on the primary side so you must use hot ground as a reference for your meter. The power supply is likely ok and you have a faulty backlight ccfl or possibly a faulty ccfl high voltage transformer. If the power supply (other than the backlight circuit) was at fault you would not see an image on the screen using a flashlight.
    Unplug all the 4 ccfl's and then connect only ONE at a time to see if the individual ccfl will light ( for 2 seconds) If one does not it is likely bad.
    Last edited by R_J; 09-13-2020, 08:30 PM.

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      #3
      Re: Acer AL1916W - Two seconds to black - Voltage regulator problem?

      I tried plugging all four lights into one plug, one at a time, and they all lit up for a second or two before they went out and I turned it off to repeat. Then, when I went to try one light in each plug, one at a time, I found that the two middle plugs both do not work, but the two on the outside do. I was a bit surprised since that is one each from the two transformers if I understand correctly
      Last edited by Long AMD; 09-13-2020, 09:00 PM.

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        #4
        Re: Acer AL1916W - Two seconds to black - Voltage regulator problem?

        Check that the small blue caps are not shorted. each end of the transformer secondary feeds a lamp. The return side of CN501 goes through R524 to ground, the return sie of CN502 goes through, R521 and then d504 dual diode, one side goes to ground one sie goes through r523 to ground. This schematic should be close
        Attached Files
        Last edited by R_J; 09-13-2020, 09:44 PM.

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          #5
          Re: Acer AL1916W - Two seconds to black - Voltage regulator problem?

          I checked the resistance of all the blue capacitors on the baord. One of them for each transformer gave a reading: C506 was 624 Ohm, and C523 was 615 Ohm. All the others on the board were greater than 200kOhm.

          Actually those two capacitors are the same contacts I probed earlier, thinking I was measuring across the transformer (points S1-S1 and S2-S2 on my diagram are joined by a trace to the capacitors C506 and C523). When I did that I was following this post: https://www.badcaps.net/forum/showpo...4&postcount=14

          Comment


            #6
            Re: Acer AL1916W - Two seconds to black - Voltage regulator problem?

            Originally posted by R_J View Post
            Check that the small blue caps are not shorted. each end of the transformer secondary feeds a lamp. The return side of CN501 goes through R524 to ground, the return sie of CN502 goes through, R521 and then d504 dual diode, one side goes to ground one sie goes through r523 to ground. This schematic should be close
            Thank you for the schematic - you are right that it seems to be very close

            I think I have found a problem with the diodes D504 and D507, which seem to be associated to the problematic middle two plugs noted before when i tested the lights. Using my multimeter in diode mode, I found that these two diodes are conducting in both directions, while the other 4 diodes of the same style (D502, D503, D508, D509) are all working normally. Based on the schematic, the diode should conduct through the pin order 1-3-2. For the good diodes, I measured values close to this example:

            D502
            Pins Meas
            12 686
            13 616
            32 626
            21 OL
            23 OL
            31 OL

            Whereas, for the two bad diodes I had the following:
            D504
            Pins Meas
            12 591
            13 630
            32 630
            21 592
            23 1374
            31 1373

            D507
            Pins Meas
            12 378
            13 627
            32 672
            21 379
            23 1102
            31 1104

            I also measured a bunch of the resistors that are in the plug circuitry and didn't find anything there. For reference it's copied below
            Tag spec meas
            R521 470 466
            R524 470 469
            R510 3.3 3.29
            R523 590 592
            R528 390(1%) 381

            If I have a problem with these diodes D504 and D507, is that something that may be caused by another underlying issue? Could the diodes be replaced? They seem very small and difficult for an amateur to solder. I think maybe my best bet is to look into getting a replacement inverter board, such as this one, and solder wires to feed power from the existing supply. Is that the right approach?
            Last edited by Long AMD; 09-20-2020, 01:20 PM.

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              #7
              Re: Acer AL1916W - Two seconds to black - Voltage regulator problem?

              Originally posted by Long AMD View Post
              If I have a problem with these diodes D504 and D507, is that something that may be caused by another underlying issue? Could the diodes be replaced? They seem very small and difficult for an amateur to solder. I think maybe my best bet is to look into getting a replacement inverter board, such as this one, and solder wires to feed power from the existing supply. Is that the right approach?
              The diodes are so tiny I have no hope to read anything on them to identify what to buy if I was going to replace them, ... Does anyone know how I could find out what part I would need to buy?

              Comment


                #8
                Re: Acer AL1916W - Two seconds to black - Voltage regulator problem?

                The diodes. d504 & d507 seem to check ok, they may check different due to r523/c530. You could swap D502 or D503 for D504 and see if it makes a difference, but if you are not comfortable with de-soldering them, that might not be the way to go.
                Last edited by R_J; 09-26-2020, 11:09 AM.

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                  #9
                  Re: Acer AL1916W - Two seconds to black - Voltage regulator problem?

                  Originally posted by R_J View Post
                  The diodes. d504 & d507 seem to check ok, they may check different due to r523/c530. You could swap D502 or D503 for D504 and see if it makes a difference, but if you are not comfortable with de-soldering them, that might not be the way to go.
                  I don't actually have a soldering iron yet. I understand it is possible to work with these tiny components if i get one with a narrow tip but I don't have it yet so unfortunately I can't remove components to test off the board or swap the parts around. I was hoping to combine it with an order for some replacement parts to save on shipping costs, but I am not yet sure what parts I should order

                  I am confused why that little RC circuit connected to pin 2 of the diodes D504 and D507 would cause the multimeter to show the diodes conduct in the wrong direction across all pins? How would it affect the measurement across pins 3->1 on D504 for example?

                  PS: I will just note that compared to the circuit diagram, the plugs on my board are in a different order: CN502 and CN504 are the two "middle plugs" I mentioned above that don't work properly, and these are the plugs associated with the (possibly) failed diodes, even though CN504 is the "bottom plug" on the circuit diagram
                  Last edited by Long AMD; 09-26-2020, 11:57 AM.

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